Fraction of Inspired Oxygen, or FiO2, represents the percentage of oxygen in the air a person inhales. Room air, for instance, contains approximately 21% oxygen, meaning its FiO2 is 0.21. In medical environments, understanding and managing FiO2 is fundamental for patient care, especially for individuals requiring supplemental oxygen. Precise control over oxygen delivery helps ensure that patients receive adequate oxygenation without experiencing potential adverse effects from too much or too little oxygen.
Common Oxygen Delivery Methods
Healthcare providers frequently use several devices to deliver supplemental oxygen, each designed for different oxygen requirements. The nasal cannula is a simple device consisting of two prongs that fit into the nostrils, suitable for low to moderate oxygen needs. A simple face mask covers the nose and mouth, providing a higher flow and concentration of oxygen than a nasal cannula. For patients requiring the highest possible oxygen concentration without mechanical ventilation, a non-rebreather mask is often employed.
Estimating FiO2 by Device
Estimating the FiO2 delivered by a nasal cannula relies on a straightforward rule of thumb. Starting with room air’s 21% oxygen, each liter per minute (L/min) of oxygen flow typically adds about 4% to the inspired oxygen concentration. For example, a patient receiving 1 L/min of oxygen via nasal cannula would inhale approximately 25% FiO2 (21% + 4%), while 2 L/min would equate to about 29% FiO2.
A simple face mask delivers a moderate range of FiO2, generally between 35% and 50%. The specific concentration depends on the oxygen flow rate, with higher flows yielding greater FiO2. Typically, a flow rate of 5 to 6 L/min might provide around 40% FiO2, while 8 to 10 L/min could deliver closer to 50% FiO2.
The non-rebreather mask is designed to deliver the highest possible FiO2 short of intubation and mechanical ventilation. This mask features a reservoir bag and one-way valves that prevent exhaled air from mixing with the oxygen in the bag. When the mask is properly fitted and the oxygen flow rate is set sufficiently high, usually 10 to 15 L/min, it can provide an FiO2 ranging from 80% to 95%.
Real-World Influences on FiO2 Delivery
The actual FiO2 a patient receives can differ from these estimations due to various real-world factors. A patient’s breathing pattern, including their respiratory rate and tidal volume (the amount of air inhaled or exhaled in one breath), significantly influences oxygen dilution. For instance, a patient taking deep, slow breaths might entrain less room air, potentially receiving a slightly higher FiO2 than estimated. Conversely, rapid, shallow breathing can lead to greater entrainment of room air, effectively diluting the oxygen concentration and lowering the delivered FiO2.
The fit of the oxygen delivery device also plays a role in the actual FiO2. A loose-fitting simple face mask or non-rebreather mask allows more room air to enter, reducing the intended oxygen concentration. Similarly, if a patient using a nasal cannula breathes through their mouth, some of the oxygen may not be effectively inhaled, leading to a lower actual FiO2. Equipment issues, such as kinks in the oxygen tubing or a partially deflated non-rebreather bag, can impede oxygen flow and compromise delivery.